An impregnation process of a porous support including immersing the support in an aqueous colloidal dispersion of ionomeric (per)fluorinated polymer, containing suiphonyl fluoride groups and having a concentration greater than 15% by weight, thermal treatment at 200 C. or less, conversion of the ionomer sulphonyl groups into the corresponding salts, ionomer crosslinking when ionomer equivalent weight is less than 650 g/eq.